1. Field of the Invention
The present invention relates to a low density parity check (LDPC) decoding technique applied in channel coding and, more particularly, to a multi-mode multi-parallelism data exchange method applied to communication systems and the device thereof.
2. Description of Related Art
Because low density parity check (LDPC) code has a powerful decoding performance close to the Shannon limit and has a characteristic of low complexity in the decoding process, it has been more and more employed in recent years, and has been widely used in many different communication applications.
The LDPC code is one kind of block codes, and defines a parity check matrix to systematically generate code words and also regulates the relationship between message bits. In algorithm, the LDPC decoding is one that transmits messages, and utilizes different algorithm to perform message reliability exchange between check node and bit node. In hardware realization, this algorithm needs to use memory for storing exchanged messages, and the required amount of memory depends on the number of 1's in the H matrix. In other words, the larger the length or the size of the H matrix, the more the required amount of memory.
Especially, in an LDPC decoder, random and large amount of message exchanges between operands cause much difficulty in realization. The quasi-cyclic LDPC coding simplifies message exchange into data shift, and therefore accomplishes a better way of circuit realization. In a quasi-cyclic LDPC decoder, shift circuits can be used for data exchange between bit node and check node because of the simplified parity check matrix. Therefore, when the length of the quasi-cyclic LDPC coding is large, in order to achieve higher data processing speed, a considerable number of shift circuits are required for data exchange actions. Because existent communication specifications need to support circuits of different shift sizes, it is possibly necessary to provide one shift circuit for each specific shift size. Moreover, because existent communication specifications have also to support different multi-mode shift sizes and multi-rate shift circuits, the shift size or hardware circuit control complexity of the quasi-cyclic coding will increase substantially, and the critical path delay of hardware circuit will increase at the same time. Besides, an ordinary shift circuit can only perform shift and exchange of a piece of data each time. Therefore, the decoding speed of the LDPC decoder cannot be enhanced for small exchange size.
A quasi-cyclic LDPC decoder requires a highly flexible shift device to provide the functions of shifters of different sizes. Accordingly, the present invention aims to provide a multi-mode multi-parallelism data exchange method and the method thereof to improve the above problems in the prior art.